Non-aqueous secondary batteries having a high energy density, such as lithium ion secondary batteries, have been widely used as power supply for portable electronic devices such as lap-top computers, mobile phones, digital cameras, and camcorders. Further, in recent years, since these batteries have a high energy density, application of these batteries to automobiles and the like has also been studied.
In conjunction with reductions in size and weight of portable electronic devices, the outer casing of a non-aqueous secondary batteries has been simplified. Non-aqueous secondary batteries initially had a battery can made of stainless steel, but a battery with an aluminum can has been developed, and further, currently a battery with a soft pack made of an aluminum laminate pack has also been developed. In the case of a soft pack outer casing made of aluminum laminate, since the outer casing is soft, joining between an electrode and a separator becomes inappropriate during charging and discharging. This may cause a technical problem of reducing the cycle life. From the viewpoint of addressing this problem, a technique for bonding an electrode and a separator becomes important, and many technical proposals have been made nowadays.
As one of such techniques, a separator in which an adhesive layer formed of a polyvinylidene fluoride resin is stacked on a polyolefin microporous membrane that is a conventional separator, has been proposed. The adhesive layer formed of a polyvinylidene fluoride resin favorably bonds to the electrode, when such an adhesive layer with an electrolyte contained therein and an electrode are subjected to heat pressing, and the adhesive layer formed of a polyvinylidene fluoride resin has a function of an adhesive that joins the electrode and the separator together. Accordingly, the cycle life of a soft pack battery can be favorably improved. In view of such a background, various technical proposals for a separator have been made in the past.
For example, in Patent Document 1 to Patent Document 3, from the viewpoint of achieving both the ensuring of sufficient adhesive property and ion permeability, technical proposals focusing upon the porous structure of a polyvinylidene fluoride resin layer have been made. Further, in Patent Document 4 to Patent Document 7, from the viewpoint of ensuring sufficient adhesive property, studies on polyvinylidene fluoride resins have been made, and an appropriate coating mass and composition have been proposed.
Meanwhile, in the process of manufacturing a battery, since the handling property of a separator has a great influence on the process yield at the time of manufacture of a battery, a technique of forming a lubricating layer, that is formed of a filler, on a separator surface, to improve the slipping property, has been proposed in Patent Document 8.
Further, in Patent Document 9, a technique of producing a separator having excellent electronic characteristics and excellent safety, by using a mixture containing barium titanate as inorganic particles and a poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (PVDF-CTFE) as a binder polymer has been proposed.
Moreover, in Patent Document 10, a separator manufactured by coating, on a polyolefin substrate, a coating liquid containing silica particles, polyethylene particles, and a PVDF/acryl water-dispersion, and then drying the coating liquid has been proposed.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2003-86162    Patent Document 2: JP-A No. 2009-70609    Patent Document 3: JP-A No. 2003-77545    Patent Document 4: JP-A No. H11-260341    Patent Document 5: JP-A No. H10-172606    Patent Document 6: JP-A No. H10-177865    Patent Document 7: JP-A No. H10-189054    Patent Document 8: JP-A No. 2010-244875    Patent Document 9: Japanese National-Phase Publication No. 2008-524824    Patent Document 10: JP-A No. 2011-171290